Photographic method and apparatus utilizing a direct-view-type storage tube

ABSTRACT

A photographing method wherein the distributed image of an object to be photographed is initially stored in the form of a stored charge density pattern on the surface of a direct-viewtype storage tube target and this pattern is then reproduced on the screen of said storage tube as a visible image which in turn is reproduced on a photographic film. In the production of the image, the value for a bias voltage to be applied to the target of the storage tube is caused to change continuously or gradually from a level at which no pattern area can be reproduced, no matter how high the stored charge density is, up to a level at which all the pattern areas are reproducible at the same time, whereby the higher the stored charge density of a pattern area is, the longer the exposure time of a film becomes (with a consequent increase in the amount of exposure). According to this method, a well-contrasted picture is obtainable through a very simple operation.

United States Patent PHOTOGRAPI-IIC METHOD AND APPARATUS UTILIZING A DIRECT-VIEW-TYPE STORAGE TUBE 6 Claims, 7 Drawing Figs.

US. Cl 95/12,

250/65, 250/213 VT Int. Cl G03b 29/00 Field of Search 95/12;

250/65,2l3 VT Km 1H Primary Examiner-Samuel S. Matthews Assistant Examiner-Monroe H. Hayes AttorneyCraig, Antonelli and Hill ABSTRACT: A photographing method wherein the distributed image of an object to be photographed is initially stored in the form of a stored charge density pattern on the surface of a direct-view-type storage tube target and this pattern is then reproduced on the screen of said storage tube as a visible image which in turn is reproduced on a photographic film. In the production of the image, the value for a bias voltage to be applied to the target of the storage tube is caused to change continuously or gradually from a level at which no pattern area can be reproduced, no matter how high the stored charge density is, up to a level at which all the pattern areas are reproducible at the same time, whereby the higher the stored charge density of a pattern area is, the longer the exposure time of a film becomes (with a consequent increase in the amount of exposure). According to this method, a well-contrasted picture is obtainable through a very simple operation.

6 DIRECT-VIEW TYPE STORAGE TUBE COMPUT/NG PHOTO TUBES /3 SCI/VT/LLATOR L? Mum HOLE COLL/MA TO? PATENTED JAN! 3 5?? SHEET 2 OF 4 0 CHARGE as/vs/rr N INVENTORS KENTI ISHIMATSM a MILE/40 mam/4r ATTORNEYS PHOTOGRAPI'IIC METHOD AND APPARATUS UTILIZING A DIRECT-VIEW-TYPE STORAGE TUBE The present invention relates to a photographing method utilizing a direct-view-type storage tube and an apparatus used in such method, and more particularly to a photographing method and apparatus well suited to cause the density distribution of objects to be represented in the form of changes in the amount of exposure or color tones of a picture image.

If the spatial distribution of objects which cannot be seen directly with the naked eye is permitted to be displayed as a visual image by some means or other so that the spatial density distribution of the objects may be observed from the brightness distribution or color tone changes in this visual image, this will facilitate the observation of the state of the spatial distribution of the objects of the quantitative changes thereof.

For instance, by way of an example of the application of radioactive isotopes in the field of medicine, there has been a method wherein a medicine in which a radioactive isotope has been incorporated and which tends to accumulate in or become attached to a specific internal organ or diseased part is taken by a patient so as to cause such isotope to collect in or attach to a specific region, in the body (e.g., the specific organ or diseased part), whereby by externally detecting the gamma ray emitted from this isotope, the distribution of the isotope in the body is observed to thereby permit the diagnosis of the organ or diseased part. In this method, an image pickup device known as a isotope camera" has been employed to provide a display of the spatial distribution of the gamma ray source (isotope) which is the object to be displayed.

The image pickup method which was hitherto used with this isotope camera has beenv such that a gamma ray information emitted from the object to be photographed (-y-ray source) is received by a scintillator which in turn emits, from the point of incidence of the received gamma ray, a light (scintillation light) whose quantity is proportional to the intensity of the incident gamma rays, the light signal thus emitted is converted by a photoelectric tube into an electrical signal which is then applied to a brightness modulation terminal of a cathode-ray oscilloscope to modulate animage electron beam simultaneously deflecting the electron beam in accordance with the radiant point of the scintillator, whereby a bright spot whose brightness corresponds to the intensity of the incident gamma ray is presented on the oscilloscope screen at the point which corresponds to the said incident point of the gamma ray; and a plurality of bright spots produced successively on the screen are picked up in sequence on a film.

According to this method, although it is not possible to make simultaneous observation of all the bright spots presented on the screen in succession, every bright spot is recorded on the film in succession so that a picture is obtained in which the degree of exposure varies in accordance with the density distribution of these spots of light. Thus, the density distribution of the gamma ray source may be determined through the contrast of the picture.

However, the drawback of the image pickupmethod according to the above conventional photographingis that the contrast in the picture image and the intensity ratio of the gamma ray source do not accurately correspond to each other because of the gamma characteristic of the film. In other words, due to the blackening saturation characteristic. in relation to the degree of film exposure, there is a reduced contrast in the highly exposed portion (i.e., where the gamma ray intensity is high) thus making it impossible to accurately recog nize very small differences in the degree of exposure (i.e., slight differences in the gamma ray intensity) in this portion.

Another drawback of this conventional method using photography is that the distribution of gamma ray source as a whole can be observed only after the film has been developed and thus it cannot be viewed directly on the screen. The result is that not only is it inconvenient to apply this method to such uses as emergency diagnoses and the like because of the considcrablc time required for developing or printing a film, but

also there isinvolved very difficult work indetermining the proper exposure time according to the gamma characteristic of a film use before taking a photograph.

Another image pickup method which has hitherto been practiced utilizes a direct-view-type storage tube in place of a cathode-ray oscilloscope. In this method, an output signal (picture signal) from a photoelectric tube in the aforesaid isotope camera is stored on the storage target surface of a direct-view storage tube in the form of stored charge-denisty so that by scanning thistarget surface with an image reproducing electron beam, a distribution image of an object to be photographed (y-ray source) is reproduced on the screen. However, although this method permits direct viewing of a distribution of a signal source (y-ray source), an object to be picked up, on the fluorescent screen of a storage tube, it is also disadvantageous in that due' to the saturation characteristic in the brightness of the imageon the fluorescent screen related to the stored charged density on the target, the contrast in the image is reduced in the proximity of this brightness saturation value so that it is no longer possible to recognize slight changes in the signal quantity.

The present invention is intended to eliminate the aforesaid drawbacks of the conventional image pickup methods and apparatus, and therefore, the principal object of the present invention is to provide an improved photographing method and an apparatus utilizing a direct-view type storage tube by which it is possible to obtain a picture of extremely good contrast, with the degree of exposure being. changed in association with and following the changes over a wide range of the density of objects to be picked up.

A further object of the present invention is to provide an improved photographing method and an apparatus utilizing a direct-view-type storage tube such that the said contrast in the picture is arbitrarily and freely adjustable.

Still further object of the present invention is to provide a novel photographing method and an apparatus in which the said contrast in a picture is converted into and displayed in the form of a difference in color tones.

To achieve the aforementioned objects, the-present invention provides a photographing method utilizing a direct-viewtype storage tube, said method comprising the steps of; storing a distribution image of an 'object to be photographed on the target surface of the direct-viewtype storage tube in the form of a stored charge density pattern, thereafter reproducing'said.

pattern on the screen of said-storage tube as a visible image, and recording said visible image on photographic film, characterized in that a bias voltage to be applied to said target is changed between one value at which no area of said pattern is reproducible and another value at which the whole areas of said pattern is simultaneously reproducible, so that the amount of exposure of the photographic film is more increased in areas of said pattern where the stored charge density is higher. 1

Another feature of the present invention resides in that the rate of change of a target bias voltagefor a storage tube is made wholly or partially adjustable as desired, whereby the contrast in an image to berecorded is made wholly and partially adjustable as desired.

Further feature of 'thepresent invention resides in that the color tone (i.e., wavelength of the light projected on an image recording medium is changed in proportion on an image recording medium is" changed in proportion to the change of a target bias voltage for a'storage tube so that the difierence in density of an object to be photographed is presented as the difference in color tone in a picture.

Further objects and'features of the present invention as well as the actions and effects resultingtherefrom will become selfevident from a detailed description'of the invention which will be made hereinafter in conjunction with a preferred embodiment of the present invention and with reference to the accompanying drawings, in which;

FIG. 1 is aschematic diagram showing a fundamental construction of an isotope camerawhich is one of the most suitableapplications of the present invention.

FIG. 2 is a longitudinal sectional view showing a schematic construction of a direct-view-type storage tube used in the present invention.

FIG. 3 is a curve showing an example of the brightness characteristic of a fluorescent screen against the stored charge density on a storage target surface.

FIG. 4 is a curve showing also an example of the relationship between the density distribution of stored charge on the storage target surface of a direct-view storage tube and the target bias voltage.

FIG. 5 is a block diagram showing a basic circuit construction of a major portion in one embodiment of the present invention.

FIG. 6 is a schematic diagram showing a basic construction of an essential portion of another embodiment of the present invention.

FIG. 7 shows a series of waveforms which indicate relationship among signals to various circuit components of the circuits shown in FIGS. 5 and 6 to explain the operations of these circuit components.

While the following explanation is given by way of an example, with respect to the application of the photographing method of the present invention to an isotope camera which is one of the most suitable applications of the present invention, it should be noted that the scope of application of the present invention will not be limited to this embodiment alone.

FIG. 1 shows the fundamental construction of an isotope camera according to an embodiment of the present invention and numeral 1 in this figure designates a signal source (y-ray source) which is an object to be photographed. In other words, the direct object is the distribution image of gamma ray radiation density (i.e., the density distribution image of an isotope which is a gamma ray source) and the object containing this gamma ray source (e.g., internal organs or affected parts of a patient) is an indirect object to be photographed. Picture signals emitted from the gamma ray source 1, that is, gamma rays are projected onto a scintillator 3 through a multihole collimator 2. This multihole collimator 2 comprises a block of a gamma ray shielding material, such as tungsten and lead, through which are formed a plurality of elongated parallel holes (collimator holes) 21. Thus, of the gamma rays emitted from the source 1, only those which are parallel to the collimator holes are permitted to enter into the scintillator 3. A crystal of sodium ionide, for example, is utilized as the scintillator 3 which produces light of a specific wavelength when the gamma rays passing through the collimator 2 strike the scintillator. This luminous phenomena is known as scintillation. The number of photons generated by the scintillator 3 is proportional to the density of the incident gamma rays. Therefore, the radiation density distribution (i.e., scintillating frequency distribution) is proportional to the density distribution of the gamma ray source. In this way, the picture signals are converted from gamma ray signals to optical signals. These optical signals are then converted into electrical signals E, by a number of phototubes 14 associated with the scintillator 3. That is, on the reverse side of the scintillator 3 (on the side opposite to the side of gamma ray incidence) there are disposed a number of phototubes with their light-receiving sides placed in close contact with the reverse side of the scintillator so that each of the phototubes generates electrical pulse signals E, which are equal in number to the incident photons on the light receiving side thereof. The output signals E,, are then applied to a computing circuit 5 where the accurate radiation points of the photons in the scintillator are determined with respect to their corresponding output pulses on the basis of the relative positional relation of respective phototubes to the whole. As a result, one signal pulse I (intensity modulation signal) and two pulse signals V and V, (deflecting voltages) having crest values corresponding to X and Y co-ordinate values of the radiation points of the photons are provided for each of the photons. (For further details in this respect, see: IEEE Transactions on Nuclear Science,.Vol. NS-l3, No. 3, June 1966, Sensitivity, Resolution and Linearity of the Scintillation Camera, by Hal 0. Anger.)

After the picture signals have been converted from optical signals into electrical signals in the manner described above, these electrical signals are stored by a direct-view-type storage tube 6 on the surface of its storage target in the form of a stored charge-density pattern which is in turn reproduced as a visible image on the fluorescent screen of the storage tube.

FIG. 2 shows diagrammatically the construction of the direct-view-type storage tube 6 in which numeral 6] designates a glass casing; 62, 63 and 64, electron guns adapted for recording, reproduction and erasing purposes, respectively; 65 a fluorescent screen; 66 a storage target. Numeral 67 is a collector screen and 68 an anode forming a parallel electron lens system together. The fluorescent screen 65 consists of a transparent substance on its surface on the target'side, and the storage target 66 consists of a metal mesh (c.g., a nickel mesh with a mesh spacing of5 to 10 meshes per millimeter) and a thin layer of insulating material such as calcium fluoride is formed on the mesh by evaporation whose thickness is of the order of several microns.

With the arrangement described above, the operation of the storage tube will be explained briefly assuming that the cathode potentials of the electron guns 62, 63 and 64 are l,000 v., 0 v. and 5 v. respectively and the potentials of the fluorescent screen 65, collector screen 67 and anode 68 are +5,000 v., +1 ,000 v. and +200 v., respectively, as shown in the figure.

Now, if the value for a voltage E, to be applied to the storage target terminal T,, i.e., target bias voltage, is set to +5 v. while the target 66 is being irradiated uniformly on its entire surface with a flood beam e, from the reproducing electron gun 63, the surface potential of the thin layer of insulating material deposited on the target mesh is balanced at 0 v. If the target surface is scanned in this state with an erasing electron beam e it results in the erasing of the charge stored on the target surface. Then, if the target bias voltage E, is returned to 0 v. in this state, the surface potential of the thin insulating layer is uniformly set to 5 v. In this instance, the flood beam e, is entirely reflected from the storage target 66 in front thereof and the flood beam does not reach the fluorescent screen 65 so that no image appears on the fluorescent screen.

When the electrical signals I, V, and V,, are applied to an intensity modulation terminal T,-, horizontal deflection terminal T, and vertical deflection terminal T respectively, the recording electron beam e, is emitted from the recording electron gun 62 in a pulselike form and this beam e, is deflected by the deflecting voltages V, and V, respectively, to scan the positions on the storage target surface which correspond to the scintillating points in the scintillator and cause electric charges to be stored at these points. In other words, a charge density pattern is formed on the surface of the thin insulating layer of the target, the pattern being proportional to the scintillation frequency distribution of the scintillator or the density distribution of the gamma ray source which is the signal source. In this way, the storage or writing of the picture signals is effected.

With the charge density pattern being formed on the target surface in the manner described above, the flood beam e, from the reproducing electron gun 63 passes through the target 66 in accordance with the stored charge density of the target surface to strike the fluorescent screen 65. This forms a visible image having an intensity distribution which corresponds to the stored charge density pattern on the target surface.

In the past, such visual image was, in that condition, considered as indicating the density distribution of the gamma ray source which was the object to be picked up or photographed. Thus, it was viewed directly on the fluorescent screen, or it was recorded on a photographic film with a camera, thereby reading the distribution of the gamma ray source, the object to be picked up, from the intensity distribution of the visible image on the screen or the photographed image thereof.

However, as previously explained the density distribution of the gamma ray source to be picked up cannot be said to accurately correspond, in fact, to the intensity distribution of the visible image reproduced on the fluorescent screen of this direct-viewstype storage tube. That is, if the target bias voltage E, is maintained at a certain value in a direct-view-type storage tube, a characteristic curve B(Nc) indicating the relationship between the stored charge density Nc on the target surface and the brightness B of the image on the fluorescent screen represents the saturation characteristic. As a result, if the stored charge density is above a certain value Ncs, the brightness presents saturation value Bs so that no further increases in the stored charge density can produce any rise in the brightness. For this reason, the brightness of the image on the screen shows almost no change when the stored charge density is in the area close to its saturation value i.e., the highdensity area of the gamma ray source) and therefore it is no longer possible to distinguish within this area any density changes of the gamma ray source as the changes in the brightness of the image. It is evident that if an image on the screen having such a saturated brightness is photographed as such, only a low-contrast picture image will be obtained as far as the high-brightness area is concerned.

According to the present invention, when photographs of such an image on the fluorescent screen are to be taken, the bias voltage to be applied to the storage target is changed gradually or continuously within the exposure time of an image recording medium, such as a photographic film or the like, whereby the higher the brightness of an image area is corresponding to the higher stored charge density area on the target surface, the longer exposure time is selected for the image recording medium to thereby achieve a photographic image which provides aproper contrast on the whole.

For this photographing purpose, a photographic camera 7 is disposed facing the fluorescent screen 65 of the storage tube 6. Here, light L emitted from the fluorescent screen 65 enters charge density), the potential on the target surface is uniformly at a level below the cutoff voltage so that the reproducing electron beam (flood beam) e, is entirely repelled from the surface of the target and no image area is reproduced on the fluorescent screen. If the voltage E, is then raised to e,, only a partial area S, ofthe stored charge pattern including the peak P of the stored charge density allows the passage of the reproducing flood beam e, thereby merely reproducing this area on the fluorescent screen as a visible image. As the voltage E, is further raised gradually to e e e,,, the pattern area which will be reproduced as a visible image also increases from S,+S,, S,+S +S;,, S,+S +S,,. Thus, it will be seen that as the target bias voltage E, becomes higher and higher, still more pattern areas with decreasing stored charge density are reproduced as a visible image. However, this results in a low-contrast image because the relative brightness in the highintensity areas of the reproduced image is reduced in inverse proportion to the increase in the target bias voltage.

On the other hand, if the target bias voltage is changed to 2,, e e e,, and the shutter of a camera is kept released all this while, only the S, area is exposed on photographic film when E,-e,; the S,+S area is exposed when E,=e,; and when E,=e,,, the S,+S +S, area is exposed. in short, the film is exposed repeatedly as often as it is concerned with such areas as correspond to the higher stored charge density areas and this increases the amount of exposure for these areas. Mathematically, this will be explained below.

That is, if I is the holding time at the nth target bias voltage e B ,(e-), B (e-), B (e B -(e the brightness of each of the areas 8,, S S S which at this time are to be reproduced (where B ,(e-)a B (e-)= B (e-): EB Q O), the amount of exposure in each of the areas 5,, S S S,, on the film are the camera through the opening of an iris 72 and is focused on a photographic film 71 by means of a lens 74. Disposed in back of the iris 72 is a shutter 73 which is adapted to open or close by a shutter release mechanism.

According to the present invention, in effecting this process of photographing, the bias voltage applied to the target of a storage tube is gradually changed from a level below that of the cutoff voltage at which no portion of the image may be reproduced so that it tends to become more positive. Consequently, the stored charge pattern on the target surface is reproduced such that those areas where the stored charge densities are high will be the first to be reproduced and those where such densities are low will be the last, whereby the degree of exposure for the film is increased in proportion to the intensity of the stored charge density.

FIG. 4 illustrates the relationship between the charge density pattern stored on the target surface of a direct-view-type storage tube and the target bias voltage; FIG. 4(a) showing in section and FIG. 4(b) in a plan view. The principle of the present invention will be explained in conjunction with these figures.

Now assume that the target bias voltage E, is changed from a sufficiently negative voltage e,, (i.e., below cutoff voltage) to e,, e e e,, so that it becomes gradually more positive. Then, each time the voltageis changed the area of the image to be reproduced also changes in proportion to this change in voltage (that is, the area is I gradually expanded). in other words, when the target bias voltage E, is e, (e, e,., where e, is cutoff voltage with respect to the peak value N of the stored Comparison between the expressions (1) and (2) indicates that the expression (2) (the exposures of the respective areas in the photographic image by the prior art method) completely agree with the last term (i.e., that portion of the expression 1 enclosed with a broken line) of the expression l (the exposures of the respective areas in the photographic image by the present invention). As is evident from the foregoing, the method according to the present invention ensures the increased amount of exposure for the higher brightness areas as compared to the prior art methods. Accordingly, where the density difference in that portion on the target surface in which the stored charge density is high cannot be recognized as the difference in the brightness of an image reproduced on the fluorescent screen e.g., where B ,(e,.)=B (e,,) in the expressions (l) and (2),) such a density difference can be definitely recognized on the film as the difference in the amount of exposure.

Calculated on the basis of the expression l the difference in exposures of the respective image areas, such as betweenareas S, and S becomes If SI( 2) S2( 2)1 s1( 3) s2( a), SI( n) S2( n) because of saturation in brightness, the amount of exposure for S, area is greater than that of 8, area by B ,(e,)-t,. Similarly, there is a difference in the amount of exposure between the areas S and S by at least B (e )-t In other words, there is a difference in the amount of exposure between the Nth area and the following area by at least B,,--(e- )-r,,-. It is evident from this that the difference in the amount of exposure among the respective areas varies according to the values of brightness B ,,(e and exposure time t Such difference in the amount of exposure can thus be adjusted as desired by suitably adjusting the values for the aforesaid target bias voltages e,, e e e, and their holding times t,, t t r,,. This ensures that contrast in a given area of the image can be freely adjusted. In the expression (1), for example, the difference of exposure of area S, with respect to area S may be increased by making the value of B,,-,(e,)-t, larger thus intensifying the contrast in S, area. This can be done by increasing the value of the target bias voltage e, to make B ,-,(e,) larger and/or by making the value oft, larger.

While it has been explained with respect to one instance in which the target bias voltage is gradually changed to 2 e,, e e e,,, it will be readily understood that the number of n steps can be made sufficiently large to make the difference between the respective steps to be sufficiently small and that the target bias voltage can be changed continuously over a desired range.

It also goes without saying that although the foregoing explanation has been made in conjunction with the target bias voltage which is changed to be more positive with respect to its initial negative value, this bias voltage may be changed conversely so that it becomes more negative with respect to its initial positive value. In the case of the latter, the results obtained will be the same as the former, though the area of an image reproduced on the fluorescent screen will be gradually reduced.

It will be now apparent from the foregoing that the present invention is extremely effective, for example, in observing the distribution of an object to be picked up or photographed which permits no direct viewing because, when an image (charge density pattern) stored on the target surface of a storage tube is reproduced on the fluorescent screen and photographs of the thus reproduced image are to be taken, the bias voltage applied to said target is changed, within the exposure time of the photographic film used, between a value e (below the cutoff voltage value) at which no image area will be reproduced on the screen and a value e,, at which any image area may be permitted to be reproduced on the screen,

whereby any wide range changes in the charge density of said pattern may be positively recognized as the changes in the amount of exposure on the film.

Now, a specific embodiment of an apparatus designed to work the method of-the present invention will be described by way of an example.

FIG. shows the circuitry of an essential part in an embodiment of the present invention, in which numeral 8 designates a shutter releasing mechanism adapted to operate the shutter 73 of the camera 7 shown in FIG. 1 and T, a target terminal of the direct-view-type storage tube illustrated in FIG. 2.

Numeral 9 designates an instruction pulse generator for initiating photographing action, the generator being composed of a monostable multivibrator or blocking oscillator, for example, and adapted to generate one instruction pulse Pc (See: FIG. 7(a)) each time a button switch 8,, is depressed. This instruction pulse P, is applied to a shutter driving pulse generator l5, cutoff voltage generator 10 and functional voltage generator II, respectively.

The shutter driving pulse generator 15 is composed ofa flipflop circuit, for example, and is adapted to generate a shutter driving pulse P, (See: FIG. 7(b)) when it receives an instruction pulse P, and a reset pulse P, (See: FIG. 7(e)). This means that this square-wave driving pulse P, a square-wave pulse which rises upon receipt of an instruction pulse P, and falls upon receipt ofa reset pulse P, and has a pulse width T.

The cutoff voltage generator 10 may be composed ofa flipflop circuit and generates a signal voltage E (See: FIG. 7(c)) upon receipt of an instruction pulse P, and a reset pulse P, (See: FIG. 7(/)). That is, this signal voltage is a negative square wave pulse voltage (pulse width T-l-Pr, peak value e,) which falls upon receipt of an instruction pulse P, and rises upon receipt ofa reset pulse P,'.

The functional voltage generator 11 may be composed of a mirror circuit, bootstrap circuit, relaxation oscillator or the like and it provides, upon receipt of an instruction pulse P,, a signal voltage E, whose value changes with time (e.g., to rise). This signal voltage may have any given functional waveform (for example, it may be a stepped waveform, linear function, quadratic function or exponential function waveform or the waveform shown in FIG. 3); but a sawtooth waveform such as shown in FIG. 7(d) will be best suited for the purpose and therefore the signal will be explained as such hereinafter. This sawtooth waveform signal voltage, when it has reached its predetermined peak voltage e,, is returned to its initial zero potential as the circuit is reset by a reset pulse P,.

The signal voltages E, and E, produced in the above described manner are then added by an adding circuit 12 to provide a sum voltage E, (See: FIG. 7(g)) which is in turn applied to the target terminal T, as a target bias voltage.

Numeral 13 designates a reset pulse generator which may comprise a built-in comparator which compares a signal voltage E, from said functional voltage generator 11 with a comparison DC voltage 2; and when the two voltages agree (i.e., when the signal voltage has attained the predetermined value e produces a negative reset pulse P, as shown in FIG. 7(e).

Numeral 14 designates a delay circuit which is adapted, upon receipt of a reset pulse P,, to produce a reset pulse P, which is delayed by a time T than the reset pulse P,. The circuit may be composed of combination of a monostable multivibrator adapted to be triggered by a negative reset pulse P, to produce a negative square-wave pulse and a differentiator circuit of this square-wave pulse so that the output pulse (positive pulse) of the differentiator circuit corresponding to the square-wave pulse at its trailing edge (of the rising portion) is delivered as the reset pulse P,'.

The shutter releasing mechanism 8 may be of an electromagnetically operated mechanism. Themechanism is so designed that it utilizes an electromagnet adapted to be energized by said shutter driving pulse P, to open and close the shutter 73 at the instant the said pulse rises and falls.

With the construction described above, the depression of the button switch 8,, generates an instruction pulse P, which in turn releases the shutter 73. The time during which the shutter is being released is T and a photographic film is exposed during this time. While on the other hand, the target bias voltage E, to be applied to the target terminal T, of the storage tube 6 is gradually raised so that it becomes more positive with respect to cutoff voltage -e,. Thus, when the target bias voltage is at the cutoff voltage e,, no portion of the charge pattern stored on the target surface is reproduced. If the target bias voltage is slightly raised from this state, that portion of the pattern where the stored charge density is highest is first caused to be reproduced on a fluorescent screen. Thus it will be seen that during the early stage of the initiated exposure operation, those pattern areas where the stored charge densities are high may be reproduced on the fluorescent screen as a visible image, but none of those pattern areas with lower stored charge densities are reproduced on the screen. As a result, only such portion of the film 71 as corresponding to the higher density pattern area is exposed at this time and thus no exposure is made on those portions which correspond to the remaining lower density pattern areas. However, as the target bias voltage E, is raised, the reproduced pattern areas gradually extend to the lower stored charge density areas with corresponding increase in the exposed film portions. When the target bias voltage has reached the predetermined peak value (61-6,), the whole pattern areas are reproduced as a visible image so that the entire portions on the film corresponding to the whole pattern areas are exposed at the same time. In other words, the values for the cutoff voltage -e, and the peak value e, of the sawtooth voltage should be predetermined in such a manner as to attain the above described results.

In this way, those portions of the film which correspond to the higher density pattern areas are subjected to correspondingly longer exposures than those portions being subjected to the larger amount of exposure. A photographic image thus obtained is characterized by a sharp contrast with respect to the whole pattern areas.

When the target bias voltage E, has reached the predetermined peak value (e e a reset pulse P, is generated which in turn closes the shutter 71 and resets the functional voltage generation circuit, whereupon the target bias voltage E, is returned to the cutoff voltage. This is a preventive measure against the occurrence of any unnecessary exposure during the closing process of the shutter. The bias voltage E! is then returned to zero potential when the cutoff voltage generator 10 is reset by a reset pulse p, developed with a time delay 1' to a reset pulse P,. The time duration 1' may be a very short period of time provided that the closing operation of the shutter 73 is completed in this time.

The procedures described above completes a single process of photography. However, according to the image pickup and photographing method utilizing a direct-view-type storage tube according to the present invention, a charge density pattern of an object once stored on the target surface can be repeatedly reproduced on the fluorescent screen as a visible image, which means that the image can be taken repeatedly, Such being the case, this method is well suited to cases where further rephotographing is necessitated by the failure of the first single photographing, or where retaking of the image is desired under different photographic conditions (with regard to the exposure time T and the light responsive speed of a film used and the like).

According to the present invention, it is also possible to display, before and after photographing, the image of an object to be photographed (i.e., the stored charge pattern on the target surface) on the fluorescent screen of a storage tube as a visible image. Thus, by observing such a visible image on the screen, proper judgement may be made prior to taking the actual photograph as to whether any modification of the contrast is needed.

It should be noted that if the voltage buildup rate of the output voltage E, (sawtooth voltage) from the functional voltage generator 11 in the circuitry arrangement of FIG. 5 is made variable, the exposure time T of film may be freely adjusted by changing this voltage buildup rate. In addition, the peak value e, of the output voltage E, from the cutoff voltage generator may be advantageously selected so that it is freely changeable in response to the peak value N of the stored charge density. It is also useful to arrange matters so that the peak value e, of the sawtooth voltage E, is changeable in accordance with changes in the cutoff voltage -e,. With such prearrangements, the variable range of the target bias voltage E, may be selected as desired. Still further, the functional voltage generator 11 may be made into an arbitrary function generator to provide an output voltage whose waveform is freely changeable. This makes the rate of change of the target bias voltage E, freely adjustable with time.

Referring to the embodiment shown in H6. 5, the delay circuit 14 may be eliminated if the cutoff voltage generator 10 is replaced by a negative DC voltage source (with output voltage --e,.). In this instance, the target bias voltage E, will be as shown in FIG. 7(h) and therefore exactly the same effects are obtainable as the previously described embodiment. It will also be advantageous if the output voltage (e,.) of this DC voltage source is made variable.

Also in the embodiment of FIG. 5, if the shutter driving pulse generator 15 is composed of a self-resettable circuit (e.g., a monostable multivibrator which produces, upon receipt of an instruction pulse P,, a square-wave pulse P, having a predetermined duration T), the application of a reset pulse P, to the pulse generator 15 will no longer be needed. Further, the reset pulse generator 13 may be eliminated if the functional voltage generator 11' is composed of a so-called self-resettable type adapted to operate in such a manner that it is returned automatically to zero potential when its output voltage E, has reached the predetermined peak value e,.

Moreover, if the shutter releasing mechanism 8 is composed of an automatic shutter mechanism such as used in ordinary cameras wherein the shutter is released the instant a shutter release signal is depressed and the shutter is automatically closed after the predetermined exposure time T has elapsed, the shutter driving pulse generator may be eliminated by causing the instruction pulse P, to be sent directly to the shutter driving mechanism to electromagnetically depress a shutter releasing button.

It should be understood from the foregoing that the specific construction of the apparatus according to the present invcntion may be suitably modified without departing from the spiritand the scope of the subject matter of the present inventron.

It is thus evident from the foregoing that according to the present invention a charge density pattern stored on a target surface corresponding to the density distribution of an object to be photographed is recorded as a high contrast photographic image. It is important to note here that the amount of exposure on film is positively changed in proportion to changes in the stored charge density, despite the saturation characteristic of brightness of an image reproduced on the fluorescent screen of a storage tube.

Another embodiment of the present invention will be explained hereinafter, which relates to a photographing method wherein an image of an object stored on the target surface of a direct-view storage tube in the form of a charge density pattern is recorded as a natural color photograph whose color tones vary in accordance with the variations of the stored charge density, that is, the density variations of the object.

In this method wherein a visible image reproduced on a fluorescent screen is photographed while the target bias voltage is being changed with the releasing time of the previously described shutter, the range of wavelength of incident light on a photographic film (color film) is changed in proportion to changes in the aforesaid target bias voltage.

In order to work this method, it is desirable to prearrange a fluorescent layer of the fluorescent screen of a storage tube so that visible light (fluorescence) emitted from the screen inclines toward white light as far as possible. It will be needless to say that the use of color film as a photographing film is required. To change the wavelength bandwidth of the incident light on this color film, an optical filter system must be disposed between the fluorescent screen and the color film to change the wavelength bandwidth of the light transmitted through the filter system. To this end, a plurality of filter elements each adapted to transmit light within a different and specific wavelength bandwidth may be used in turn or an interference filter adapted to continuously change the bandwidth of the transmitted light may be used. In short, it is essential to cause the wavelength bandwidth of light transmitted through this filter system to change continuously or gradually following changes in the target bias voltage.

FIG. 6 shows diagrammatically the arrangement of the essential part in one embodiment of the apparatus for working the above described method. In the figure, a filter system 20 is disposed between a fluorescent screen 65 of a storage tube 6 and a camera 7. The filter system 20 comprises a plurality of filter elementsf f fl, .f,, which are disposed and supported circumferentially on a rotary supporting disk 21 in regularly spaced relation. The disk 21 is adapted to be rotated by a filter changing mechanism 17 through a power transmission mechanism 18 so that it rotates about a shaft 19 by a predetermined rotational angle so as to bring the plurality of these filter elementsf f f .f,, in front of the camera 7 successively as the disk rotates. The filter changing mechanism 17 may be composed of a pulse motor which is adapted to be rotated a certain angle for each input pulse received, that is, a driving pulse P, (See: FIG. 7(i)) from a filter changing pulse generator 16. The filter changing signal generator 16 is designed so that it receives target bias voltage E, (See: FIG. 7(g)) and generates driving pulses P P P P, (See: FIG. 7(i)), respectively, when the received signal E, coincide with the predetermined voltages 6,, e e e,,. For this purpose, the generator 16 may be composed of a comparator.

With the arrangement described above, assume that the shutter 73 is released with the filter element f, being in front of the camera 7. Then, light is emitted from those pattern areas which are to be reproduced while the target bias voltage E, (See: FIG. 7(3)) changes from e to e 1 and the light is passed through the filter element f to fall on the color film 71. When the voltage E, coincides with e,, a driving pulse P as shown in FIG. 7(1') is generated thus changing the filter element from f to f Similarly, light emitted from those pattern areas reproduced while the voltage E changes from e to e is transmitted through the filter element f to expose the color film 71. Repetition of the same process successively changes the filter elements as the target bias voltage E, changes and this results in the corresponding changes in the wavelength of light that falls on the color film. Thus, a photograph taken on the film provides a color photographic image in which color tones vary in proportion to the variations in the stored charge density. With the photographic image thus obtained, the stored charge density or the density variations of the object may be readily determined from the variations of tones in the image.

Listed below are the remarkable effects which are attributable to the method and the apparatus of the present invention which have been discussed above in detail:

I. An image of an object to be photographed which is stored on a storage target surface in the form of a stored charge density pattern can be photographed on film with a good contrast. Since the contrast of such photographic image is freely changeable with respect to any area thereof, simplified recog nition is provided by emphasizing the contrast of any desired image areas.

2. Simplified means of recognizing the density variations of an object is provided because the distribution of density of an object is presented not only in the form of a monochromatic image but also in colored form.

3. Photographing operation is very simple because it is only required to simply change the target bias voltage during the shutter releasing time or to cause the target bias voltage and the transmission bandwidth of filters to change in associated manner. Thus, there is no need for any particularly complicated apparatus and the operation itself is extremely simple.

Although the present invention provides a photographing method which is best suited for use with the previously discussed isotope camera, generally it will be also effective in all the applications where an image of an object which prohibits direct-viewing thereofis first stored on a direct-viewtype storage tube and it is then reproduced as a visible image.

For example, if the contrast of an image is deteriorated on a radar system because of the increased noise components due to snow fall, the present invention may be advantageously used to store such video signals for a long period of time so that these signals may be reproduced as a photographic image to thereby cancel the noise components and obtain well-contrasted distinct pictures which permits positive recognition of the target involved.

What we claim is:

l. A photographing method utilizing a direct-view-type storage tube having a storage target, said method comprising the steps of: storaging a distribution image of an object to be photographed on the storage target surface of the direct-viewtype storage tube in the form of a stored charge density pattern, thereafter reproducing said pattern on the screen of said storage tube as a visible image, and recording said visible image on photographic film during a continuous exposure period, characterized in that during said continuous exposure period a bias voltage to be applied to said storage target is changed between one value at which no area of said pattern is reproducible and another value at which the whole area of said pattern is simultaneously reproducible, so that the amount of exposure of the photographic film is greater in areas of said pattern where the stored charge density is higher. 2. A photographing method according to claim I characterized in that said target bias voltage is changed from one value at which no area of said pattern is reproducible up to another value at which the whole area of said pattern is sim ultaneously reproducible such that said bias voltage is changed and raised continuously and linearly so as to be more positive with respect to the starting voltage.

3. A photographing method according to claim 1 characterized in that the wavelength of incident light to the photographic film is changed in accordance with changes in the target bias voltage.

4. A photographing apparatus with a direct-view-type storage tube comprising a direct-view-type storage tube including a storage target adapted to store and reproduce an image of an object to be photographed, a photographic camera disposed opposite the screen face of said storage tube, means to release the shutter of said camera only during a predetermined time upon reproduction of an image recorded on the target surface of said storage tube in the form of a stored charge density pattern, and means to apply to the target of said storage tube a bias voltage having a value which changes between one value at which no area of said image is reproduced and another value at which the whole area of said image is reproduced entirely during the releasing time of said shutter.

5. A photographing apparatus according to claim 4 characterized in that said means to change the target bias voltage comprises a cutoff voltage generator to produce a sufficiently negative DC voltage so that no image area is reproduced, a functional voltage generator to provide a voltage of a given waveform, the peak value thereof being equal to the difference voltage between the maximum and minimum of the variations of said bias voltage, and an adding circuit adapted to add up the output voltages of said two generators.

6. A photographing apparatus according to claim 4 characterized in that a filter system is disposed between the screen and the photographic camera, said filter system including a plurality of interchangeable filter elements, and means is provided to change said plurality of filter elements in accordance with changes in said target bias signal. 

1. A photographing method utilizing a direct-view-type storage tube having a storage target, said method comprising the steps of: storaging a distribution image of an object to be photographed on the storage target surface of the direct-viewtype storage tube in the form of a stored charge density pattern, thereafter reproducing said pattern on the screen of said storage tube as a visible image, and recording said visible image on photographic film during a continuous exposure period, characterized in that during said continuous exposure period a bias voltage to be applied to said storage target is changed between one value at which no area of said pattern is reproducible and another value at which the whole area of said pattern is simultaneously reproducible, so that the amount of exposure of the photographic film is greater in areas of said pattern where the stored charge density is higher.
 2. A photographing method according to claim 1 characterized in that said target bias voltage is changed from one value at which no area of said pattern is reproducible up to another value at which the whole area of said pattern is simultaneously reproducible such that said bias voltage is changed and raised continuously and linearly so as to be more positive with respect to the starting voltage.
 3. A photographing method according to claim 1 characterized in that the wavelength of incident light to the photographic film is changed in accordance with changes in the target bias voltage.
 4. A photographing apparatus with a direct-view-type storage tube comprising a direct-view-type storage tube including a storage target adapted to store and reproduce an image of an object to be photographed, a photographic camera disposed opposite the screen face of said storage tube, means to release the shutter of said camera only during a predetermined timE upon reproduction of an image recorded on the target surface of said storage tube in the form of a stored charge density pattern, and means to apply to the target of said storage tube a bias voltage having a value which changes between one value at which no area of said image is reproduced and another value at which the whole area of said image is reproduced entirely during the releasing time of said shutter.
 5. A photographing apparatus according to claim 4 characterized in that said means to change the target bias voltage comprises a cutoff voltage generator to produce a sufficiently negative DC voltage so that no image area is reproduced, a functional voltage generator to provide a voltage of a given waveform, the peak value thereof being equal to the difference voltage between the maximum and minimum of the variations of said bias voltage, and an adding circuit adapted to add up the output voltages of said two generators.
 6. A photographing apparatus according to claim 4 characterized in that a filter system is disposed between the screen and the photographic camera, said filter system including a plurality of interchangeable filter elements, and means is provided to change said plurality of filter elements in accordance with changes in said target bias signal. 